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University of California. 



[Vol. 2. 



like those in the gabbro. The character of the rock through which 

 the so-called veins pass, has no effect upon their mineralogical com- 

 position. It is very difficult to tell which are true dikes and which 

 are veins of segregation. In this vicinity are the most striking and 

 sudden changes in texture, structure, and composition. Portions of 

 the same eruptive mass show as great variations in a very short 

 distance as might be expected from wholly distinct masses. 



The wehrlite passes up the hill back of Point Morrito, constitut- 

 ing much of that promontory, but the outcrops are poor. South 

 of the hill and along the coast east of the Chute the formation 

 changes considerably. The wehrlite is replaced by a dark apha- 

 nitic serpentine (dunite), which is traversed by many branching 

 irregular dikes of diabase. 



The first canon east of the Chute gives a clean section across 

 the complex, which is here about 1,000 feet wide. The upper por- 

 tion consists of gabbro for several hundred feet, with a small amount 

 of diabase. There seem to be different intrusions here, but their 

 relations are not plain. Below these is a belt of altered dunite 

 extending to the ocean. It has a uniform appearance, except near 

 the sea, where it contains a small amount of feldspar and enstatite. 

 Just above the water it is intersected by many narrow dikes of 

 diabasic character, and at one spot by a dike of wehrlite. East of 

 the spot where this gulch enters the ocean, a prominent dike of 

 diabase runs parallel with the cliffs for a quarter of a mile. The 

 clean cut contacts with the serpentine show that it is intrusive, a 

 fact which is also corroborated by the character of the dike. It is 

 fine and almost porcelain-like on the edges and coarser in the 

 middle. It adheres so firmly to the serpentine that, instead of 

 parting at the real junction, the separation is about two inches 

 within the serpentine. In addition to the large dike, which is fre- 

 quently 12 feet in diameter, there are numerous smaller ones. 

 The serpentine here is generally massive, showing lamination only 

 in spots. The exceedingly irregular and bunchy nature of these 

 dikes explains how it is that when shearing has affected the serpen- 

 tine, the dikes are broken up into boulder-like masses, which, in the 

 most of the serpentine areas in the Coast Ranges, are so difficult of 

 explanation. 



